1. Field of the Invention
This invention relates to systems for positioning a cover over a space and more particularly to systems for positioning a cover over a swimming pool.
2. State of the Art
Swimming pools are often covered when not in use for reasons which include restricting access, limiting evaporation of water and chemicals, retaining heat and acting as a barrier to leaves, twigs and similar kinds of material. Other spaces such as ponds and other kinds of pools may also be covered from time to time for similar reasons.
A wide variety of covers are available to cover such spaces. For example, covers for swimming pools include both manual covers that are manually positioned, opened and fastened, automatic covers that are operated between open and closed configurations by a motor or similar drive mechanism, and semiautomatic mechanisms that may be automatic in one direction and manual in the other direction. U.S. Pat. No. 3,050,743 (Lamb) discloses an early automatic cover typically used with swimming pools. A more recent version of an automatic cover is disclosed in U.S. Pat. No. 4,858,253 (Lamb).
As can be seen in the '253 Patent, the automatic cover system therein illustrated and described has tracks along two opposite edges of the pool. The tracks guide the edges of the cover and guide the ropes which extend outwardly from the leading edge around pulleys and back to reels. A motor is connected through a clutch to drive the drum to wind the cover to the open position and to drive reels that pull in the ropes to urge the cover to the closed position. The clutch has a sacrificial pin which will break before other damage can be inflicted on the ropes or cover. The reels are positioned in a housing which has pulleys to guide the ropes from the tracks to the reels. The pulleys are positioned so that the ropes each impose a torque or twisting force which typically elastically deflects the housing during movement of the cover from the closed to the open position. That is, the housing is fabricated from plate metal that is capable of elastic deflection and is mounted so that twisting or deflecting is not inhibited.
The track has a slot or groove to accept the outside edges of the cover and a separate slot or groove to guide the rope back to its respective reel. The outside edges of the cover sometimes encounter resistance as they slide in their respective grooves, both when opening and closing. That is, corrosion, dirt, dimensional variance or a host of other factors, separately or in some combination, may restrict the movement of one or the other or both outside edges of the cover in its respective slot. Thus, when closing the cover, the motor continues to drive the reels and wind the rope even if the cover is stuck. In turn, the tension in the rope increases. The rope is made of elastically deformable material such as polyester. As the force or tension increases, the rope stretches in length. That is, the rope stretches considerably and is believed to stretch about 17 percent per unit length in many situations. As the motor driving the wheel which is winding the rope continues to operate, the force exerted by the rope on the cover in the track increases to a point where the force is sufficient to overcome the frictional increase and the cover begins to move through or past the particular location. The cover may even accelerate in speed for a short distance until the rope tension (energy stored in the rope) diminishes to a normal or typical level or magnitude. In operation, covers have been observed moving in a jerking or intermittent fashion along one or both edges as the edge encounters different points of high friction along the length of the track. In some cases, one edge of a cover may move much farther that the other edge so that the cover may become cocked or diagonally disposed between two substantially parallel tracks and in turn jammed in place.
Due to friction in the track, the ropes for both sides of the prior structural stretch or elongate as the cover is positioned over the pool. When the cover reaches the end of the pool or space to be covered, the motor is shut down by a switch. As the motor shuts down, the torque or force applied to the ropes by the motor ends. In turn, the energy in the rope allows some of the rope to pay back from its respective reel so that some covers have been observed "jumping back" from the edge leaving a gap between the cover and edge of the pool. Depending on the degree of friction, it can also be seen that the force exerted by the rope may be sufficient to cause a sacrificial pin in the clutch to fail to avoid tearing the cover or breaking one of the ropes.
Covers of the type illustrated and disclosed in the '253 Patent also may from time to time over wind or wind up more than required and in turn cause either one or both of the cover edges to come out of the slots of their respective tracks. That is, the rope provided is usually longer than the distance from the front edge of the cover in the open position to the pulley and back to the reel because the rope is typically cut longer and also because the rope inelastically deforms or stretches and in turn gets longer after installation. Excess rope is typically wound on the reel with as may as four or five revolutions of rope being observed in some cases for new ropes and more for older ropes. Further, it has been observed that one of the two ropes for a pool cover may stretch more than the other thereby changing the radius of the rope and the number of revolutions of the rope on the reel for any given position of the cover. Thus, the ropes for the opposite sides will tend to wind and unwind at different rates even though the reels both operate at exactly the same revolutions per minute. In turn one side travels faster than the other to contribute to misalignment of one side with respect to the other side particularly after repeated use. Thus the front edge or leading edge of a cover may become cocked to other than normal or generally perpendicular to and between the tracks. In addition a cover with one rope longer than the other can become misaligned so that one edge can pull out of a track and require user servicing to repair.
With the ropes longer than the distance from the front edge of the cover in the open position to the reel, there is excess rope on both sides that allows the cover to be over driven. Thus, the user needs to carefully re-thread the cover outside edges into their respective slots in order to avoid damage to the cover and to resume normal operation. Of course, the cover can be over driven even if the rope is sized in length to be the same as the distance from the front edge of the cover to the reel because the rope is elastically deformable. Accordingly, if the motor is not timely turned off, it can over drive the cover and cause one or both of the opposite edges of the cover to be pulled out of their respective tracks. Upon subsequent operation, there is a risk of damage to the cover and the track as well as to other components of the system.
Some covers have an automatic shut off feature. A magnet is attached to one outside edge of a cover proximate its front edge. As the cover approaches the closed position, the magnet triggers or operates a reed switch attached to the track. The reed switch sends a signal that turns off the motor to stop the cover at the closed position. If the cover has become misaligned with the edge with the magnet sticking so that its associated rope is tensioned more and elongates more, it can be seen that the edge opposite to the edge with the magnet will reach its end first. Thereafter, the motor will continue to drive the related reel and tension the rope. Alternately the side without the reed switch can stick so that the side with the reed switch continues to advance and eventually reaching the position in which the reed switch operates. The motor then turns off leaving the pool cover cocked in a less than fully closed position.
An automatic shut off feature may be provided for the open position as well. That is, the magnet may activate a reed switch at the other end of the track and turn off the motor as the cover reaches the open position. If one edge sticks and the other does not, it can be seen that one edge can pull out or the motor can turn off before the cover reaches the fully open position.
A cover system is needed that does not jam and that does not skip or jump along the track. A cover system is needed that does not jump back from the closed position and that does not disengage one or both of the edges of the cover from their respective tracks when the cover reaches the open position. A cover system is needed that does not lead to a cocked orientation and servicing to realign to keep the cover with its front edge oriented generally normal to the tracks.